The present invention relates to a new and improved method and apparatus for controlling the air-fuel ratio at a burner.
The air-fuel ratio at a burner has previously been controlled by using impulsed regulators to keep the fuel and air pressures equal. If the two pressures are maintained equal, the fuel and air flow rates are maintained proportional throughout a range of firing rates. However, this system is ineffective if the density of the air varies during operation of the burner.
A known system for controlling the characteristics of a main burner flame includes a control burner which is supplied with the same gas/air mixture as the main burner. The heat released from the control burner is sensed and the gas/air mixture is varied to keep the total heat released by the control burner constant to thereby maintain the heat released by the main burner constant. This system is disclosed in U.S. Pat. No. 3,407,022. Other systems utilizing auxiliary burners to control the flow of fuel to working burners are disclosed in U.S. Pat. Nos. 2,780,414 and 2,366,170. Known systems for controlling air-fuel ratios are disclosed in U.S. Pat. Nos. 2,866,602 and 3,493,005.